Uncertainty Analysis For Super-Accuracy Fizeau Interferometer

In order to make an exposure system for 193nm lithography projection objective and to meet the requirements of figure accuracy for optical elements in the system, it is indispensible to possess a super-accuracy phase-shifting Fizeau interferometer which can reach the accuracy on the level ofλ/50 (PV) andλ/300 (RMS). The research was made on the firstΦ100mm horizontal Fizeau interferometer and aimed at achieving super-accuracy figure metrology; in this case an interferometer optical system was designed as a simulation tool, and further focuses on several factors which would have effects on the interferometer accuracy through the use of FEM analysis, Monte-Carlo algorithm and experiments. These factors contain self-gravity deformation of the etalon, ratracing error in the cavity, reference figure error, refractive index change in the cavity and a few instrument errors.The main work of this paper could be divided into the following parts: First, the basic principle of the interferometer and its functional parts of were deeply analyzed, and relative analysis results were offered; moreover, an optical system for horizontal Fizeau interferometer was designed with an aperture 102mm and resolution 1024 by1024, which would result in a super-accuracy figure metrology. Second, along with FEA method, two supporting types-adhesive support and retainer support for the etalon were provided, with which the effect of etalon on the transmitted wavefront was investigated through the transform of Zernike polynomials. The conclusion shows that both types were feasible but the RMS value using adhesive support was much better. Third, a mathematical equation with respect to the ratracing error which resulted from the tilt of transmitted wavefront was established when testing spherical surfaces, and the analysis shows that ratracing error decreases when the radius of curvature increases for spherical surfaces, and a sensitivity function method was created for compensating the metrology accuracy. Forth, a calibration method using a rotating ball was investigated, and this method was used to calibrate an F#1.5,Φ100mm reference surface. The calibration result was similar to the designed accuracy ofλ/30 (PV); in addition, some significant experience was obtained. Fifth, through the experimental data from the lab, effects of different parameters including temperature, pressure and relative humidity on the change of index were investigated and the effect of index change in the cavity on figure metrology were further analyzed through the use of Monte Carlo algorithm, which would offer enviremontal control data for achieving super-accuracy interferometric metrology. Finally, uncertainty propagation law was employed to combine several error sources in the paper and an uncertainty budget was given.